Electric motors have existed for many years. Today, some electric motors are designed with a rotor disposed radially outward of the stator. These motors are commonly referred to as “inside-out” or “external rotor” electric motors and are typically of the three-phase induction type. External rotor electric motors have many applications, typically commercial or industrial, such as for fans, pumps, machine drives, etc. Furthermore, with the advent of single-to-three phase electronic converters, three-phrase external rotor motors can also be used in residential applications and other environments limited to single-phase electric service.
Typically, the stator of an external rotor electric motor includes coils (or windings) for each phase that are inserted through slots of the same size and shape positioned along the periphery of the stator at a single radius. As a result, the coils are bundled together and cross-over or overlap each other resulting in lengthy coil wire usage, high heat generation requiring additional copper and metal materials for dissipation, and high magnetic losses causing low electro-mechanical efficiency. Additionally, the typical stator design limits the motor speed options, which is a function of the number of slots that can be positioned on the periphery of the rotor.
Accordingly, it is seen that a need exists for a stator for external rotor electric motors that avoids coil wire bundling and cross-over and offers more flexibility for the number of slots to overcome the foregoing consequences. It is to the provision of such therefore that the present invention is primarily directed.